The human spine is a biomechanical structure with thirty-three vertebral members, and is responsible for protecting the spinal cord, nerve roots and internal organs of the thorax and abdomen. The spine also provides structural support for the body while permitting flexibility of motion. A significant portion of the population will experience back pain at some point in their lives resulting from a spinal condition. The pain may range from general discomfort to disabling pain that immobilizes the individual. Back pain may result from a trauma to the spine, be caused by the natural aging process, or may be the result of a degenerative disease or condition. Similarly, neck pain may occur in related ways, i.e., from injury, aging or disease.
The intervertebral disc functions to stabilize the spine and to distribute forces between vertebral bodies. A normal disc includes a gelatinous nucleus pulposus, an annulus fibrosis and two vertebral end plates. The nucleus pulposus is surrounded and confined by the annulus fibrosis.
It is known that intervertebral discs are prone to injury and degeneration. For example, herniated discs are common, and typically occur when normal wear, or exceptional strain, causes a disc to rupture. Degenerative disc disease typically results from the normal aging process, in which the tissue gradually looses its natural water and elasticity, causing the degenerated disc to shrink and possibly to rupture. These conditions often are treated with the use of intervertebral implants.
In particular, areas of the cervical spine and the lumbar spine are particularly prone to the need for intervertebral implants, or artificial disc implants because they are areas where the spine is particularly dynamic. Thus, the implants that are used often are dynamic or motion-preserving implants. There are challenges, however, with dynamic implants and when there are problems, comes poor performance. For example, maintaining the stability of dynamic implants in the disc space, or merely preventing such dynamic implants from backing-out of the disc space after they are surgically inserted are some such challenges.
There, therefore, is a need to increase the stability of dynamic implants in the disc space and also a need to prevent backing-out of such devices after they have been implanted. Further, there is a need to do so without the use of anchors or flanges on the disc and the need for extra preparation of the endplates of the vertebrae for such extra features.